Effects of minority-carrier response behavior on Ge MOS capacitor characteristics: Experimental measurements and theoretical simulations

In this paper, we present MEDICI simulations of the admittance-voltage properties of Ge and Si MOS devices, including analyses of substrate conductance G_sub and high-low transition frequency f_tran, to explore the differences in the minority-carrier response. The Arrhenius-dependent G_sub characteristics revealed that a larger energy loss-by at least four orders of magnitude-occurs in Ge than in Si, reflecting the fast minority-carrier response rate, i.e., a higher value of f_tran. We confirmed that the higher intrinsic carrier concentration in Ge, through the generation/recombination of midgap trap levels as well as the diffusion mechanism, resulted in the onset of low-frequency C-V curves in the kilohertz regime, accompanying the gate-independent inversion conductance. The experimental data obtained from Al₂ O₃Ge MOS capacitors were consistent with the values of G_sub and f_tran obtained from MEDICI predictions and theoretical calculations. In addition, upon increasing the inversion biases, we observed shifts in the G_sub conductance peaks to low frequencies that mainly arose from the transition of minority carriers with bulk traps in the depletion layer. Meanwhile, we estimated that the bulky defects of ca. (2-4) × 10¹⁵ cm^-3 exist in present-day low-doped Ge wafers.